Add the devices to be used for development in ‘Certificates’

In Macintosh HD > Applications > Utilities > Keychain Access

Menu > Keychain Access > Preferences > Certificates > set Online Certificate Status Protocol (OSCP) and Certificate Revocation List (CRL) to “Off”.

Menu > Keychain Access > Certificate Assistant > Request a Certificate from a Certificate Authority.

‘User Email Address’ and ‘Common Name’ must match the registered iPhone Developer info

CA (Certificate Authority) Email Address: Not required. (The ‘Required’ message will be auto removed)

Request is: ‘Saved to Disk’

Let me specify key pair information: Checked

Continue

Specify file name and click Save.

Key Size: 2048 bits

Algorithm: RSA

Press Continue and the certificate request will be created.  After a few moments refreshing the browser will have the certificate available to download.

Using Issued Certificate

Download the  WWDR Intermediate Certificate.  Then double-click the downloaded cert to launch Keychain Access and install (the default Keychain: Login is fine).

Download the issued Developer Identity Certificate.  Then double-click the downloaded cert to launch Keychain Access and install(the default Keychain: Login is fine).